What this code means
B1235 may indicate that the climate control system is seeing a possible issue with the driver’s air mix control function, which is used to manage driver-side temperature blending.
What the vehicle may do
- The driver’s temperature output may be incorrect.
- The driver’s temperature control may not respond normally.
- The concern can be intermittent if wiring or connector contact is poor.
Possible fault areas
- Possible driver’s air mix control motor circuit issue.
- Possible driver’s air mix control motor issue.
- Possible linkage or air mix door issue.
- Possible climate control unit issue.
Diagnostic path
Code overview
On this Accord, B1235 points to a possible problem in the driver’s air mix control side of the climate control system. In plain terms, the system may not be able to move the driver’s temperature blend door the way it expects. The driver’s outlet temperature may be incorrect, may not respond normally, or may act intermittent. The broad fault areas can include the driver’s air mix control motor circuit, the motor itself, the linkage, the air mix door, or the climate control unit. We’re going to keep the diagnosis in order and prove the circuit before condemning a component.
Confirm the code first
Start by verifying the problem. Clear the DTCs with the HDS. Then cycle the ignition to LOCK (0) and back to ON (II), or use the engine start/stop button to go to OFF mode and then ON mode. Run the self-diagnostic with the HDS or with the climate control unit, then check for codes again. If B1235, or 42, comes right back, continue into the circuit checks. If it does not come back, treat it as an intermittent failure and check for loose wires or poor connections in the driver’s air mix control motor circuit.
Check the hot-side motor control wire for an open
Next, check the M-HOT DR, or M-HOT, line for an open. Turn the ignition to LOCK (0), or select OFF mode. Disconnect the climate control unit 32P connector and the driver’s air mix control motor 7P connector. Check continuity from climate control unit 32P connector No. 2, the PNK wire, to driver’s air mix control motor 7P connector No. 7, also the PNK wire. If you have continuity, that wire is not open, so move on. If you do not have continuity, repair the open in the wire between the climate control unit and the driver’s air mix control motor.
Check the cool-side motor control wire for an open
Now do the same open-circuit check on the M-COOL DR, or M-COOL, line. With the same connectors still disconnected and the ignition still in LOCK (0) or OFF mode, check continuity from climate control unit 32P connector No. 3, the LT BLU wire, to driver’s air mix control motor 7P connector No. 6, also the LT BLU wire. If continuity is present, that wire is not open and you continue. If continuity is not present, repair the open in the wire between the climate control unit and the driver’s air mix control motor.
Check the hot-side wire for a short to ground
After both open checks pass, check the M-HOT DR line for a short to body ground. Keep the climate control unit 32P connector and the driver’s air mix control motor 7P connector disconnected, with the ignition in LOCK (0) or OFF mode. Check continuity from climate control unit 32P connector No. 2, the PNK wire, to body ground. If there is continuity, repair the short to body ground in the wire between the climate control unit and the driver’s air mix control motor. If there is no continuity, the M-HOT DR/M-HOT wire is OK, and you move to the next check.
Check the cool-side wire for a short to ground
Next, check the M-COOL DR line for a short to body ground. With the connectors still disconnected and the ignition in LOCK (0) or OFF mode, check continuity from climate control unit 32P connector No. 3, the LT BLU wire, to body ground. If there is continuity, repair the short to body ground in the wire between the climate control unit and the driver’s air mix control motor. If there is no continuity, the M-COOL DR/M-COOL wire is OK, and the wiring checks in this path have passed.
Test the driver’s air mix control motor
With the circuit checks passed, test the driver’s air mix control motor. If the motor tests OK, replace the climate control unit. If the motor does not test OK, replace the driver’s air mix control motor, or repair the driver’s air mix control linkage or door. The key here is not to jump to the control unit until the motor circuit and motor side have been proven.
Wrap-up
For B1235, the clean path is: confirm the code, prove both control wires are not open, prove they are not shorted to ground, then test the driver’s air mix control motor before deciding whether the fault is in the motor, linkage, door, or climate control unit. For more diagnostic training, visit stepdiagnostics.com.
Final check
B1235 is best approached by confirming the code, checking the driver’s air mix motor control circuits for opens and shorts to ground, and then testing the motor side before making a control-unit call.
For more guided automotive diagnostics, visit STEP Diagnostics.
